全文获取类型
收费全文 | 4409篇 |
免费 | 471篇 |
国内免费 | 223篇 |
专业分类
电工技术 | 170篇 |
综合类 | 241篇 |
化学工业 | 868篇 |
金属工艺 | 579篇 |
机械仪表 | 294篇 |
建筑科学 | 337篇 |
矿业工程 | 74篇 |
能源动力 | 137篇 |
轻工业 | 199篇 |
水利工程 | 138篇 |
石油天然气 | 120篇 |
武器工业 | 43篇 |
无线电 | 366篇 |
一般工业技术 | 683篇 |
冶金工业 | 288篇 |
原子能技术 | 52篇 |
自动化技术 | 514篇 |
出版年
2025年 | 96篇 |
2024年 | 224篇 |
2023年 | 227篇 |
2022年 | 201篇 |
2021年 | 238篇 |
2020年 | 186篇 |
2019年 | 130篇 |
2018年 | 143篇 |
2017年 | 118篇 |
2016年 | 142篇 |
2015年 | 150篇 |
2014年 | 174篇 |
2013年 | 225篇 |
2012年 | 205篇 |
2011年 | 248篇 |
2010年 | 177篇 |
2009年 | 183篇 |
2008年 | 187篇 |
2007年 | 192篇 |
2006年 | 184篇 |
2005年 | 183篇 |
2004年 | 143篇 |
2003年 | 165篇 |
2002年 | 189篇 |
2001年 | 151篇 |
2000年 | 111篇 |
1999年 | 82篇 |
1998年 | 60篇 |
1997年 | 68篇 |
1996年 | 31篇 |
1995年 | 42篇 |
1994年 | 30篇 |
1993年 | 29篇 |
1992年 | 23篇 |
1991年 | 37篇 |
1990年 | 52篇 |
1989年 | 21篇 |
1988年 | 13篇 |
1987年 | 5篇 |
1986年 | 2篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1964年 | 1篇 |
1957年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有5103条查询结果,搜索用时 0 毫秒
1.
2.
The surface chemistry of methoxide (CH3O-) on the Ni(111) surface has been studied in the presence of hydrogen pressures up to 2 Torr. During heating in vacuum methoxide decomposes to H2 and CO, which desorb at 380 and 445 K, respectively. The CH3O-decomposition process is rate limited by CH bond breaking and exhibits a strong deuterium kinetic isotope effect in CD3O-. In the presence of ambient hydrogen pressures of 0.02–2.0 Torr both CH3O- and CD3O-are hydrogenated directly to methanol at 310 K. Methoxide is hydrogenated by adsorbed hydrogen, which nearly saturates the surface at these pressures and temperatures. 相似文献
3.
ECN树脂中的可水解氯含量是决定树脂质量的—个重要指标。本文研究了反应温度、ECH/OCN配比、反应时间和碱用量等因素的影响,取得了规律性的认识,并获得最佳配方,制备出高纯度的ECN树脂系列产品。 相似文献
4.
5.
6.
SUNZhencui CAOWentian WEIQinqin WANGShuyun XUEChengshan SUNHaibo 《稀有金属(英文版)》2005,24(2):194-199
Hexagonal GaN films were prepared by nitriding Ga2O3 films with flowing ammonia. Ga2O3 films were deposited on Ga-diffused Si (111) substrates by radio frequency (r.f.) magnetron sputtering. This paper have investigated the change of structural properties of GaN films nitrided in NH3 atmosphere at the temperatures of 850, 900, and 950℃ for 15 min and nitrided at the temperature of 900℃ for 10, 15, and 20 rain, respectively. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were used to analyze the structure, surface morphology and composition of synthesized samples. The results reveal that the as-grown films are polycrystalline GaN with hexagonal wurtzite structure and GaN films with the highest crystal quality can be obtained when nitrided at 900℃ for 15 min. 相似文献
7.
Jaffee Sara R.; Caspi Avshalom; Moffitt Terrie E.; Taylor Alan 《Canadian Metallurgical Quarterly》2004,113(1):44
The well-documented finding that child physical maltreatment predicts later antisocial behavior has at least 2 explanations: (a) Physical maltreatment causes antisocial behavior, and (b) genetic factors transmitted from parents to children influence the likelihood that parents will be abusive and that children will engage in antisocial behavior. The authors tested these hypotheses in the representative Environmental-Risk cohort of 1,116 twin pairs and their families, who were assessed when the twins were 5 and 7 years old. Mothers reported on children's experience of physical maltreatment, and mothers and teachers reported on children's antisocial behavior. The findings support the hypothesis that physical maltreatment plays a causal role in the development of children's antisocial behavior and that preventing maltreatment can prevent its violent sequelae. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
8.
介绍FRS-12S-14.5/3.82-450型余热水管锅炉以较少的投资、较少的工程量、较短的施工周期改造成QF35/1050-14.2-3.82/450型火管锅炉,使热力系统满足了120kt/a硫磺制酸装置的工艺要求。改造后系统运行平稳,运行率提高,维护费用减少,生产成本降低,解决了水管锅炉因换热管束爆管导致锅炉腐蚀及烟气泄漏造成的环境污染等问题。 相似文献
9.
10.
Variation in structural and dielectric properties of co-precipitated nanoparticles strontium ferrites due to value of pH 总被引:2,自引:0,他引:2
Nanoparticles of strontium ferrites with nominal composition SrFe12O19 were prepared by co-precipitation method, by decreasing pH from 13 to 8 with a regular step of 1. The secondary phase of α-Fe2O3 was increased with the decrease in pH. The crystallite size estimated from X-rays diffraction data was in the range 52-70 nm, which is much smaller than that already reported. Most of the particles formed had hexagonal structure, as observed by the scanning electron microscopy. Particle size and dielectric loss were increased where as dc electrical resistivity and dielectric constant were decreased with decrease in pH. The results show that the material synthesized with higher pH is phase pure and is potentially more suitable for high frequency applications. 相似文献